The present invention relates to a front passenger seat airbag apparatus that inflates and deploy an airbag in front of a front passenger seat to protect an occupant seated in the seat from an impact when the impact is applied to the vehicle from the front.
Typically, a front passenger seat airbag apparatus is provided in a part of the instrument panel of a vehicle that corresponds to the front passenger seat. In a case where the instrument panel is formed of a hard resin, the following type of front passenger seat airbag apparatus can be employed. That is, an airbag deployment opening is provided in the instrument panel, and the airbag deployment opening is closed by a lid body formed separately from the instrument panel. However, a gap or a step is inevitably formed between the lid body and the instrument panel in this apparatus, which degrades the appearance of the interior of the vehicle. Further, since the lid body, which is formed separately from the instrument panel, needs to be installed, the number of steps for installing the airbag apparatus is increased.
In this respect, front passenger seat airbag apparatuses having a lid body integrally formed with the instrument panel have been proposed (for example, refer to Japanese Laid-Open Patent Publication No. 2008-37282). FIG. 19 shows a cross-sectional structure of an airbag apparatus of this type, and FIGS. 20(A) to 20(D) show a process in which the airbag is inflated and deployed. As shown in FIGS. 19 and 20, a base member 103 of an instrument panel 102 has an split-opening portion 101 on a back surface (lower surface as viewed in FIG. 19). The split-opening portion 101 can be opened and broken when the airbag is inflated and deployed. The split-opening portion 101 is formed by two transverse breakable portions 104, two front-rear breakable portions 105, and a middle breakable portion 106.
The transverse breakable portions 104 are arranged along the front-rear direction of the vehicle and extend substantially along the transverse direction of the vehicle (in a direction perpendicular to the elevation of FIG. 19). The two front-rear breakable portions 105 are arranged along the transverse direction of the vehicle, and extend substantially along the front-rear direction of the vehicle. The two transverse breakable portions 104 and the two front-rear breakable portions 105 are connected to each other to substantially form a rectangle. The middle breakable portion 106 is located between the two transverse breakable portions 104 and extends along the transverse direction of the vehicle to be connected to the front-rear breakable portions 105. The middle breakable portion 106 thus divides the rectangle formed by the breakable portions 104, 105 into two front and rear rectangles.
Two portions of the base member 103 that are surrounded by the transverse breakable portions 104 and the front-rear breakable portions 105 and divided into front and rear parts by the middle breakable portion 106 are referred to as door portions 107F, 107R. A portion of the split-opening portion 101 that is close to the outer side (a portion about the split-opening portion 101) is referred to as a door adjacent portion 108. The door adjacent portion 108 is supported by a frame portion 109 provided on its back surface. The door portions 107F, 107R are supported from the back by a pair of door support portions 111F, 111R, which are arranged along the front-rear direction in the frame portion 109. The door support portions 111F, 111R are coupled to the frame portion 109 by a pair of front and rear hinge portions 112F, 112R.
In the front passenger seat airbag apparatus 113 configured as described above, when an impact is applied to the vehicle from the front, for example, due to a frontal collision, inflation gas is supplied to an airbag 114, which is in turn inflated while being unfolded. With the inflation, the pressing force of the airbag 114 acts on the front and rear door portions 107F, 107R through the front and rear door support portions 111F, 111R. The pressing force breaks the breakable portions, thereby separating the front and rear door portions 107F, 107R from the door adjacent portion 108. The front and rear door support portions 111F, 111R are pivoted upward about the hinge portions 112F, 112R, together with the door portions 107F, 107R, and are opened forward and rearward, respectively. This creates an airbag deployment opening 115 for the airbag 114 in the instrument panel 102 (see FIG. 20(D)).
However, in the front passenger seat airbag apparatus 113, in which the instrument panel and the lid body are integrally formed, the breaking strength of the breakable portions 104, 105, 106 is substantially the same in a normal condition. On the other hand, when the airbag 114, which has been folded by a common folding method, is inflated while being unfolded, pressing force generated by the inflation of the airbag 114 applied to the middle breakable portion 106 is greatest in the base member 103. Thus, in the split-opening portion 101, the middle breakable portion 106 is first broken (see FIG. 20(B)). Then, the front-rear breakable portion 105 and the transverse breakable portion 104 are broken (see FIGS. 20(C), 20(D)). When the split-opening portion 101 is broken in this manner, the door support portions 111F, 111R start pivoting about the hinge portions 112F, 112R after the middle breakable portion 106 is broken and before the transverse breakable portions 104 are broken. Accordingly, the door support portions 111F, 111R and the door portions 107F, 107R are pivoted in small radii while the transverse breakable portions 104 is being broken. As a result, the door portions 107F, 107R interfere with the door adjacent portion 108 in the vicinity of each transverse breakable portion 104. This can cause the door portions 107F, 107R or the door adjacent portion 108 to crack or shatter.
Under low-temperature environment, for example, during wintertime, the brittleness of the base member 103 is increased and the above described phenomenon is more likely to occur. Since the hinge portions 112F, 112R shrink and are hardened under low-temperature environment, the radii of rotation of the door portions 107F, 107R are not expected to be increased. This also can promote the cracking and shattering.
During recent years, the weight of vehicle parts have been reduced to improve the fuel economy of vehicles. As part of the attempts to reduce the weight of the parts, the thickness of resin parts have been reduced, and the base members of instrument panels tend to be formed thinner. However, in the above described front passenger seat airbag apparatus 113, if the door portions 107F, 107R and the door adjacent portion 108 are formed to be thin, the strength of these parts are reduced, which is more likely cause the cracking and shattering.
Therefore, there is a demand for a front passenger seat airbag apparatus having a thin base member that is not easily cracked or shattered under low temperature environment.
FIG. 1 of the above cited document shows a state of the connected door portions 107F, 107R being separated from the door adjacent portion 108 by alternate long and two short dashes lines. However, the description of the documents has no explanation about this phenomenon. Also, no explanation is given as to the order in which the breakable portions are broken.
Even if FIG. 1 of the document was drafted with the intension of showing that the transverse breakable portions 104 are to be broken before the middle breakable portion 106 is broken, the specific time at which the front-rear breakable portions 105 should be broken is not clearly disclosed. The manner in which the breakable portions are broken is determined based on the manner in which the airbag 114 is unfolded and on the characteristics of the hinge portions 112F, 112R. In the apparatus of the above cited document, the cracking and shattering as described above can still be caused depending on the manner in which the breakable portions are broken.